1. Technical Field
The present invention is related to communication networks and in particular to transmission quality measurements of communication signals between distributed components of a communication network.
2. State of the Art
In distributed wireless communication systems jointly using the same frequency bands or channels, the channel actually allocated to a base station for communication with respective remote stations has to be selected. Such a channel selection can be accomplished at the instant a communication connection between a base station and a remote station is set up (e.g. DECT-systems), centralized for all base station covering a certain geographical area (e.g. GSM-systems), or at arbitrary times (e.g. HIPERLAN/2).
In the latter case, which is addressed by the present invention, the channel selection, i.e. the allocation of certain frequencies of a jointly used frequency band, is performed de-centralized and autonomously at each base station. As a result, a selected channel is not allocated to individual communication links for a base station above allocated for a base station which uses the selected channel and the frequencies contained therein, respectively, for several communication links established with this base station.
Such selections and allocations of channels and frequencies, respectively, are often controlled by methods for a so-called adaptive channel selection (ACS). ACS-methods are based on measurements of received signal strength (RSS) levels on available channels for a base station. The RSS-measurements could be performed both in the up-link (i.e. the communication link from the base station to a remote station) and in the down-link (i.e. the communication link from a remote station to the base station). The result of a RSS-measurement is indicative of signal interference for signals transmitted between the base station and respective remote stations. In particular, down-link signal interference is caused by two or more remote stations communicating with same base station within a channel commonly used, while up-link signal interference on signals transmitted by a base station can result from signal interference of signals transmitted by base stations via a commonly used channel.
On the basis of RSS-measurements being indicative of the transmission quality of available channels, the channel selection/allocation for a base station is performed. In order to select/allocate the channel having an optimum transmission quality, the above ACS-methods have to react quickly on changed/modified operational conditions within a communication network. Therefore, the actual communication situation and especially signal interference associated therewith are monitored by means of RSS-measurements. In order to obtain the actual signal interference situation, conventionally, the RSS-measurements are performed continuously. Usually, measurement periods for RSS-measurement are predefined fixed time periods both for allocated and available channels. As used in the following, a measurement period is the time between two successive measurements.
Depending on the number of allocated/available channels and the number of remote stations assigned to a base station, this can result in a large number of measurements. Since RS-measurements for down-links are usually performed by remote stations, the large number of RSS-measurements lead to an increased need of additional power resources, which is especially disadvantageous for (mobile) remote stations using batteries. Further, an increased channel transmission capacity must be provided for measurement requests and measurement reports between base stations and remote stations. Moreover, an increased load can occur for handling measurement requests, reports and results at a base station, requiring an increased processing time and capacity.
Moreover, RSS-measurements should compensate for signal fluctuations due to varying propagation losses and varying transmission power for base and remote stations, in order to provide reliable results. On one hand, this can accomplished by a large number of measurements for continuously monitoring the current interference situation, also leading to the above-mentioned problems. On the other hand, temporary fluctuations of RSS-measurements can be compensated by linear filtering. In case RSS-measurement fluctuations do not occur temporarily but persistently, the linear filtering follows the RSS-measurements with a certain delay time leading to an delayed/impaired channel selection.
3. Object of the Invention
Principally, the object of the present invention is to solve the above-mentioned problems of known communication networks. In particular, the object of the present invention is to provide a method and a system for measuring the transmission quality in a communication network requiring a reduced number of measurements (e.g. RSS-measurements).
4. Principle Underlying the Invention
In order to reduce transmission quality measurements in a communication network, the present invention is based on the principle both to adaptively control transmission quality measurements with respect to operational conditions/situations in a communication network and/or to perform transmission quality measurements providing a long term transmission quality estimation for a communication network.
5. Solution According to the Invention
In particular the invention provides a method for measuring the transmission quality between a base station and at least one remote station in a communication network having at least one channel for transferring signals between the base station and the at least one remote station. The method comprises measuring a transmission quality for signal transmissions via the at least one channel, and defining a transmission quality measurement period for the at least one channel in relation to the measured transmission quality.
Preferably, the measuring of the transmission quality includes measuring of a transmission quality for a channel allocated to the base station for communicating with the at least one remote station and/or measuring of a transmission quality for at least one channel available for the base station for communicating with the at least one remote station.
Here, it is possible to define a transmission quality measurement period for the allocated channel in relation to a ratio of the transmission quality value of the allocated channel and at least one of the transmission quality value of the at least one available channel.
Moreover, the defining of the transmission quality measurement period include defining a transmission quality measurement period for each of the at least one available channel in relation to a ratio of the transmission quality value for the allocated channel and the transmission quality value for a respective one of the at least one available channel.
As a result, the ratio for the transmission quality measurement period for the allocated channel can be a ratio of the transmission quality value of the allocated channel and the maximum transmission quality value of the transmission quality value for the at least one available channel.
In order to select an optimal channel for the base station, the transmission quality measurement period for the allocated channel and the transmission quality measurement period for the at least one available channel are compared, whereby the allocated channel can be replaced by allocating one of the at least one available channel having a larger transmission quality measurement period compared to the allocated channel.
Further, the invention provides a method for measuring the transmission quality between a base station and at least one remote station in a communication network as defined above, wherein the method comprises determining the number of remote stations associated to the base station, and defining a transmission quality measurement period for the at least one channel in relation to the number of the remote stations for measuring the transmission quality for signal transmissions between the base station and the at least one remote stations.
Since the transmission quality for remote stations being not actively communicating with the base station have a lower importance compared to the transmission quality of actively, actually communicating remote stations, it is preferred that the number of the remote stations is determined for remote stations being in communication with the base station.
Moreover, a further method according to the invention for measuring the transmission quality in the above network comprises defining grouping criteria, assigning each of the at least one remote station to one of at least two remote station sets according to the grouping criteria, and defining transmission quality measurement periods for each of the remote station sets in relation to the grouping criteria.
Preferably, the transmission quality measurement periods are indicative of a transmission quality measurement period for measuring the transmission quality of signal transmissions between the base station and the at least on remote station of a respective one of the remote station sets. As a result, only the transmission quality for one of the remote station sets are required to be measured during the respective one of the transmission quality measurement periods.
In case no information required for the assignment of the remote stations are available, parameters of the at least one remote station associated to the base station are measured. Especially, the parameters should be in correspondence with the grouping criteria.
In one embodiment, the method includes defining the grouping criteria as being indicative of at least two transmission quality ranges/groups, measuring the transmission quality for each of the at least one remote station, assigning each of the at least one remote station to one of the remote station sets according to the respective remote station transmission quality, and defining the transmission quality measurement periods in relation to a respective one of the transmission quality ranges/groups.
In a further embodiment, the method includes defining of the grouping criteria being indicative of at least two data types,
determining the data type being currently communicated between the base station and each of the at least one remote station, assigning each of the at least one remote station to one of the remote station sets according to the data type communicated to/from the respective remote station, and defining the transmission quality measurement periods in relation to a respective one of the data types.
Moreover, it is possible to combine the above embodiments. In one combination, for at least one of the remote station sets defined according to the transmission quality grouping criteria, at least two remote station subsets are defined according to the data type grouping criteria, and the transmission quality measurement periods for the at least two remote station subsets are defined in relation to the transmission quality ranges/groups and the data types, while transmission quality measurement periods for the remaining of the remote station sets not including remote station subsets are defined in relation to the transmission quality ranges/groups.
In another combination, for at least one of the remote station sets defined according to the data type grouping criteria, at least two remote station subsets are defined according to the transmission quality grouping criteria, and the transmission quality measurement periods for the at least two remote station subsets are defined in relation to the transmission quality ranges/groups and the data types, while transmission quality measurement periods for the remaining of the remote station sets not including remote station subsets are defined in relation to the data types.
As mentioned, the invention also provides for a method to perform transmission quality measurements for a long term estimation of the transmission quality. Here, the method for a communication network as described above comprises measuring of a transmission quality of transmission signals between a base station and at least one remote station via at least one channel allocated to the base station, defining of a first quality metric based on the signal strengths, measuring of a transmission quality of further transmission signals via the at least one channel of the base station, defining of a second quality metric based on the signal strength for the further transmission signals, and defining a transmission quality measurement period for the at least one channel in relation to the first and second quality metrics.
In particular, the first quality metrics is indicative of signal interference on a respective of the transmission signals caused by the base station and/or the at least one remote station, and the second quality metric is indicative of signal interference on the further transmission signals caused by the base station and/or at least one further base station. Or more particular the first quality metric is indicative of signal interference on a respective of the transmission signals caused by all interfering base stations and all interfering remote stations being active on the measured channel c, and the second quality metric is indicative of the maximum of the signal interference on the further transmission signals caused by at least one further interfering base station.
Further, it is possible to define a third quality metric as a function of the first and second quality metrics, wherein the transmission quality measurement period is defined in relation to the third quality metric.
To provide for a continuously measurement of the transmission quality, a series of the first quality metric is defined based on the signal strengths being sampled over a first period terminating at a first time, and/or a series of the second quality metric is defined based on the signal strengths being sampled over a second period terminating at a second time, and/or the third quality metric is defined at a third time on the basis of the first and second quality metric series.
For an embodiment of this method, the minimal second quality metric of the second quality metric series is determined, whereby the third quality metric can be defined as the minimum of the first quality metric most recently defined and the minimal second quality metric.
Preferably, the transmission signals are generated at the base station and/or at the at least one remote station in correspondence to communication signals being used for communication between the base station and the at least one remote stations and/or the further transmission signals are generated at the base station and/or at the at least one further base station in correspondence to communication signals thereof, the further transmission signals having a predetermined signal level, preferable the maximum signal level to be generated at the base station and/or at the at least one further base station.
For a selection of optimal channels, resulting in a further reduction of the required number of transmission quality measurements, the methods includes determining whether the third quality metric exceeds a predetermined quality level and allocating a respective channel to the base station for actual communication with the at least one remote station.
Moreover, for all above methods, embodiments can be provided, wherein the transmission quality measurement periods are set to a first predetermined transmission quality measurement period, if the transmission quality measurement periods exceed a first predetermined transmission quality threshold, and/or the transmission quality measurement periods are set to a second predetermined transmission quality measurement period, if the transmission quality measurement periods are below a second predetermined transmission quality threshold, and/or the transmission quality measurement periods are defined to be within a range between a minimal transmission quality measurement period and a maximal transmission quality measurement period.
Also, embodiments are considered, wherein transmission quality measurements are performed according to the transmission quality measurement periods, and the transmission quality measurements can be used to define new transmission quality measurement periods to be currently used.
Referring to the method according to the invention utilizing grouping criteria, it is possible to use the transmission quality measurements according to the transmission quality measurement periods to re-assign the at least one remote station to the remote station sets and/or to the remote station subsets according to a respective one of the transmission quality measurements.
Especially in the case of data type grouping criteria, it is preferred to determine data types being communicated between the base station and the remote stations in line with the transmission quality measurement periods for reassigning the at least one remote station to the remote station sets and/or the remote station subsets.
In order to consider different parameter influencing the measured transmission quality, it is considered to determine the signal strengths and/or numbers of transmission errors for signal transmissions between the base station and the at least one remote station. Alternatively the transmission quality can be assessed from measurements of the signal strength of the signal transmission between the base station and the at least one remote station and relating this signal strength measurements to the interfering signal strength.
Since the transmission situation in a communication network changes over time depending e.g. on the number of base stations jointly using channels, the number and types of communicating remote stations and the like, the measurement of the transmission quality should be adapted to fulfil varying network requirements. Therefore, the invention contemplates to arbitrarily combine the above described methods. Such combinations include the utilization of different methods according to the invention for base and remote stations, wherein each station can use different embodiments, subsequently or in parallel.
Additionally, the object of the invention is solved by a system for a communication network having at least one base station and at least one remote station transferring signals between each other via at least one channel for carrying out of one of the methods according to the invention. The system comprises measuring means for measuring the transmission quality of signal transmissions via the at least channel, means for the definition of at least one transmissions quality measurement period for signal transmissions between the base station and the at least one remote station, and control means for the measurement of the transmission quality during the at least one transmission quality measurement period.
In particular, the system can be operated with respect to the at least one channel being allocated to or available for the base station.
Depending on the network in which the system according to the invention is used, the measuring means are located at the base station and/or at the at least one remote station, the transmission quality measurement period definition means are located at the base station, the control means are located at the base station and/or at the at least one remote station, and transmission and reception means are provided at the base station and at the at least one remote station for communicating the measured transmission quality.